This invention relates generally to the automated analysis of samples (specimens) such as biological samples having microscopic features, and more specifically to the use of a flatbed scanner in such analysis.
The desirability of analyzing lymph nodes of cancer patients for micrometastatic (tumor) cells is well established, both as a indicator of patient prognosis and as a possible guide as to the advisability of treatment with adjuvant therapy (chemotherapy/hormones). Unfortunately, current practice makes it impractical to examine an entire lymph node.
Typically, a lymph node is on the order of 5 mm in length. In routine pathology this node is cut in two and embedded in paraffin. This results in two (half) nodes embedded next to each other with a depth on the order of 2.5 mm. The current practice is to take sections of this material, stained with hematoxylin and eosin (H&E) which are then examined manually by a pathologist using a conventional microscope.
Routine diagnosis on sentinel nodes is performed by cutting six 4-μm sections at one level, but a number of recent papers have highlighted the inadequacy of such an approach. It has also been suggested to use immunohistochemical (IHC) staining and examining very substantial proportions of the entire node, and increases of between 7% and 35% in positive cases were reported. Thus, the implication is that current practice is missing this number of truly positive cases. Given that the lymph node status is a key element in decisions of post-operative therapy, this is clearly cause for concern.
However, even cutting at a distance of 8 μm and examining only every other section results in more than 150 sections to be analyzed. Assuming that three sections are placed on each slide, the node requires more than 50 slides. This is clearly out of the realm of manual inspection of the samples.
Automated microscopy is well established as a significant enhancement. A conventional microscope-based scanner (CMS) uses a computer controlled stage for scanning a sample and a digital recording camera to record an image of one or several relevant microscopic fields for subsequent analysis by the computer. For example, image analysis is used to distinguish tumor cells from disturbing artifacts such as dirt, debris, or other events that resemble the cells of interest. For this process, sufficient spatial resolution is required. That is, each object needs to be described with sufficient image elements (pixels) in order to facilitate proper recognition. Whereas the effectiveness of such systems in producing reproducible results has been successfully demonstrated in a number of applications, their performance is relatively slow (typically 20 minutes to scan 1 square cm).
With a lymph node section being on the order of 5–6 mm on a side, it would take on the order of 15–20 hours to scan the 150 lymph node sections prepared as described above. Thus, even current automated scanning systems do not have the throughput to make analysis of all, or even substantial parts, of the node practical. This is disturbing since current research indicates that such information derived from a substantial part of the node would provide a potentially significant increase in clinical sensitivity.